Reversing a vehicle while towing a trailer can be challenging for many drivers, particularly for drivers that drive with a trailer on an infrequent basis or with various types of trailers. Systems used to assist a driver with backing a trailer can control various vehicle systems to attempt to keep the speed of the towing vehicle below a limit where such systems become unreliable, particularly at preventing the trailer from converging toward a jackknife angle or the like. Further advances in such systems may be desired.